Abstract: Journal of Steroid Biochemistry and Molecular Biology 213 (2021) 105964 Contents lists available at ScienceDirect Journal of Steroid Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/jsbmb Impact of vitamin D on the course of COVID-19 during pregnancy: A case control study Selcan Sinaci a, *, Doga Fatma Ocal a, Didem Fatma Yucel Yetiskin a, Derya Uyan Hendem a, Gul Nihal Buyuk a, Sule Goncu Ayhan a, Atakan Tanacan a, A. Seval Ozgu-Erdinc a, Ozlem Moraloglu Tekin a, b, Dilek Sahin a, b a b Department of Obstetrics and Gynecology, Ministry of Health, Ankara City Hospital, Ankara, Turkey University of Health Sciences, Ankara City Hospital, Ankara, Turkey A R T I C L E I N F O A B S T R A C T Keywords: COVID-19 Pregnancy Vitamin D deficiency Immune system Cytokine storm Objective: We aimed to evaluate the vitamin D status of pregnant women with COVID-19, and the association between vitamin D level and severity of COVID-19. Methods: In this case control study, 159 women with a single pregnancy and tested positive for SARS-CoV-2, and randomly selected 332 healthy pregnant women with similar gestational ages were included. COVID-19 patients were classified as mild, moderate, and severe. Vitamin D deficiency was defined as 25-hydroxycholecalciferol <20 ng/mL (50 nmol/L), and 25-OH D vitamin <10 ng/mL was defined as severe vitamin D deficiency, also 25-OH D vitamin level between 20− 29 ng/mL (525− 725 nmol/L) was defined as vitamin D insufficiency. Results: Vitamin D levels of the pregnant women in the COVID-19 group (12.46) were lower than the control group (18.76). 25-OH D vitamin levels of those in the mild COVID-19 category (13.69) were significantly higher than those in the moderate/severe category (9.06). In terms of taking vitamin D supplementation, there was no statistically significant difference between the groups. However, it was observed that all of those who had severe COVID-19 were the patients who did not take vitamin D supplementation. Conclusion: The vitamin D levels are low in pregnant women with COVID-19. Also, there is a significant dif­ ference regarding to vitamin D level and COVID-19 severity in pregnant women. Maintenance of adequate vitamin D level can be useful as an approach for the prevention of an aggressive course of the inflammation induced by this novel coronavirus in pregnant women.